This invention relates to mobile seismic energy land sources for seismic surveying of the earth, and more particularly, to a method and system for well velocity shooting and vertical seismic profiling for generating powerful seismic signals for deep penetration into the earth utilizing a single vehicle for transporting a plurality of seismic sources which may be arranged in any desired array at the well site.
Seismic exploration on land involves the transmission of strong seismic impulses into the earth's surface at a desired site. The impulses may be repeated at frequent intervals at the desired site, and a network of geophones is used to sense the results at various points on the ground spaced from the site, the signals from these geophones being recorded and/or processed. The geophones are coupled to the earth for receiving the resultant vibrational waves which have been reflected and/or refracted or otherwise affected by subsurface geologic strata and structures in the earth. Analysis of the signals from the geophones provides information about the conditions and characteristics of the geologic formations in the regions being surveyed. The geophones may also be suspended down a drilled well for providing information concerning the surrounding geologic formations and possible oil or gas bearing regions near the well.
Seismic energy land sources have been constructed in compact and mobile form provided with a tank or container which may be a dome-shaped bell, having a displaceable diaphragm at the bottom to enclose an imcompressible liquid such as water. One or more air guns are positioned within the contained liquid for suddenly releasing pressurized gas, usually compressed air, into the liquid for generating powerful seismic impulses transmitted down through the diaphragm into the earth.
Detailed information with respect to such prior mobile seismic energy land sources is disclosed in U.S. Pat. Nos. 3,310,128; 3,779,335; 3,800,907; and 4,108,271, which are assigned to the assignee of the present invention.
Such prior land seismic sources have proven to have numerous advantages in actual use. In well velocity shooting and vertical seismic profiling, there are instances where it is desirable to utilize a plurality of seismic sources in an array near the mouth of the well. When such prior land seismic sources are used, there is a vehicle associated with each source, and so an array of vehicles is required in arranging an array of seismic sources near the well. The present invention advantageously enables one vehicle to provide an array of seismic sources near a well.